1. Field of the Invention
This invention relates to a process cartridge and an image forming apparatus. Here, the term "image forming apparatus" covers, for example, an electrophotographic copying apparatus, an electrophotographic printer (e.g. an LED printer, a laser beam printer or the like), electrophotographic facsimile apparatus and an electrophotographic word processor.
Also, the term "process cartridge" refers to a combination of charging means, developing means or cleaning means and an electrophotographic photosensitive member integrally made into a cartridge which is removably mountable with respect to an image forming apparatus body, or a combination of at least one of charging means, developing means, and cleaning means and an electrophotographic photosensitive member integrally made into a cartridge which is removably mountable with respect to an image forming apparatus body, or a combination of at least developing means and an electrophotographic photosensitive member integrally made into a cartridge which is removably mountable with respect to an image forming apparatus body.
2. Related Background Art
In an image forming apparatus using the electrophotographic image forming process, there has heretofore been adopted a process cartridge system in which an electrophotographic photosensitive member and process means acting on this electrophotographic photosensitive member are integrally made into a cartridge which is removably mountable with respect to the image forming apparatus body. According to this process cartridge system, the maintenance of the apparatus can be done not by a serviceman, but by a user himself and therefore, the operability of the apparatus can be markedly improved. So, this process cartridge system is widely used in electrophotographic image forming apparatuses.
FIG. 5 of the accompanying drawings is a cross-sectional view showing an image forming apparatus on which a process cartridge according to the prior art is mountable, and shows an electrophotographic recording apparatus used as the engine of a copying apparatus or a page printer.
As shown in FIG. 5, a photosensitive drum (electrophotographic photosensitive member) 102, a charging roller (charging means) 103 and cleaning means 114 including a cleaning blade are made integrally with one another and constructed into a process cartridge (latent image process cartridge) 115, which is removably mountable with respect to an image forming apparatus body 101 through mounting means 122.
The photosensitive drum 102 is rotated in one direction about the axis thereof, and the surface of the photosensitive drum 102 is uniformly charged by a bias comprising an alternating current superposed on a direct current being applied thereto from a bias power source 104 connected to the charging roller 103. The uniformly charged photosensitive drum 102 is suitably exposed to light by an exposure device 105, so that an electrostatic latent image is formed on the surface of the photosensitive drum.
A developing device 106 is installed at a slight distance from the photosensitive drum 102, and the latent image formed on the surface of the photosensitive drum 102 is developed by the developing device 106 by the use of a developer 107 and is visualized as a toner image. The thus obtained toner image is transferred to a transfer material 110 by a transfer charger 109. The transfer material 110 is supplied from a sheet supply cassette 120 by a sheet supply roller 111, and is sent to the transfer charger 109 in synchronism with the toner image on the photosensitive drum 102 by register rollers 112.
The toner image transferred to the transfer material 110 is conveyed to a fixating device 113 with the transfer material 110 to be fixated by pressure and becomes a recorded image. On the other hand, any developer untransferred and left on the photosensitive drum 102 is removed by a cleaning blade made of an elastic material forming cleaning means 114 which is in contact with the photosensitive drum 102. The photosensitive drum 102 from which the untransferred developer has been removed is again subjected to uniform charging on the surface thereof by the charging roller 103, and the above-described process is repeated.
In such an image forming apparatus, in order to facilitate the maintenance of the apparatus, a process cartridge provided by several process elements combined together or by a single process element is sometimes made easily mountable and dismountable with respect to the apparatus. The latent image process cartridge of FIG. 5 of the accompanying drawings, i.e., a process cartridge 115 comprising the photosensitive member 102, the charging roller 103 and the cleaning means 114 made integral with one another, is an example of a combination of process elements. As an example of the single process element, there is the developing device 106 of FIG. 5 made into a developing process cartridge 116.
Of course, the combination of the process elements constituting the process cartridge is not limited to the above-described examples, but is free. Also, the latent image process cartridge 115 and a developing process cartridge 116 may be made integral with each other by frame members 117 and 118 to be made into a cartridge removably mountable with respect to the apparatus body 101.
In an image forming apparatus provided with such process cartridge, it is often the case that the nominal life of the cartridge is defined as a standard and can ensure the quality of each process cartridge, because the process cartridge is replaced when this nominal life is exceeded. In many cases, the nominal life of a process cartridge is indicated by a simple value, such as a maximum number of supplied sheets, and there has been adopted a system for warning the user when the replacement is reached by a counter or the like in the apparatus body.
However, with the advance of the function of the image forming apparatus, the form of print, i.e., the form of image formation, has become complicated (for example, image formation on both an A3 sheet and an A4 sheet is effected or a plurality of developing devices are interchanged to thereby effect multi-color image formation), and depending on the situation of use, the maximum number of supplied sheets for the process cartridge has varied greatly.
Therefore, there has been proposed a system in which the life of the cartridge is not prescribed by the conventional nominal life, but there is provided an element for storing life detection parameters, such as the integrated number of printed sheets for the process cartridge, the driving time and the electrical energization time, and the cartridge life is determined on the basis of these data. There has further been proposed a system in which a memory element, such as a non-volatile memory, is carried on a process cartridge itself, so that the cartridge life can be detected more accurately even if the cartridge is interchanged in its course of use.
Also, there are some irregularities in the physical characteristics and variations in characteristics by use in the constituents of the process cartridge. Therefore, there has been proposed a system in which an element for storing the physical characteristic of the individual constituents therein is provided in the process cartridge itself and correction is applied to image forming conditions by the image forming apparatus body. Again in this case, hysteresis such as the driving time, the electrical energization time and the integrated amount of current are sometimes stored in a memory element so that fine correction of the image forming conditions may be effected.
Now, recently, from the viewpoint of the effective utilization of natural resources, used process cartridges have been collected and reused, and cartridges carrying the memory elements therein as described above have been recycled bodily with the memory elements.
Generally, however, a memory element is limited in write-in frequency, and writing-in exceeding a prescribed frequency defined for each kind of memory element spoils the reliability of the contents of memory. When the contents of the memory deteriorate, not only do the life of the process cartridge and the image forming conditions deteriorate, but also in the worst case, the image forming apparatus body may be spoiled or get out of order.